In the manufacturing of electric and/or electronic components such as for example inductive elements like transformers, inductors or chokes, there exists an ongoing demand for devices with higher power density. However, the higher the power density of an inductive element, the lower the total losses that need to be dissipated by a smaller surface of the inductive element in order to keep the temperature rise constant. Contrary, in order to fulfill the regulations and safety requirements, insulation distances have to be increased and insulators between the coils and the core like for example plastic coil formers have to be inserted. These plastic coil formers reduce the copper fill factor, that is the ratio of the utilized and the available winding window. Therefore, the nonconductive areas typically restrict the reduction of the losses in the inductive elements.
In order to provide transformers with higher copper fill factors and lower winding losses that require only a small space, planar transformers where the windings are formed by copper traces that are etched on a printed circuit board (PCB), have been introduced. However, the copper fill factors of PCB planar transformers are limited to a certain extent. In order to carry high currents, several PCB's have to be paralleled because the thickness of the traces that can be etched on a PCB is limited. Hence, these PCB's increase the insulation space causing a low copper fill factor. Finally, they are not useful in other applications such as for example in high power, high current applications.
The document WO 03/030189 A1 shows a transformer for high power applications with enhanced quality and safety standards. Here, the primary windings are formed by a wire that is wound around a plastic bobbin, while the secondary winding is formed by at least one metal sheet that is open on one side, plugged onto the bobbin and connected to a printed circuit board.
This transformer is able to carry high currents and allows copper fill factors that are higher compared to PCB planar transformers. However, this transformer has a plastic bobbin that limits the copper fill factor tremendously and therefore has degraded electrical and/or magnetic characteristics.